1. Field of the Invention
The present invention relates to oil and natural gas production. More specifically, the system facilitates the introduction of a fluid under pressure into a wellbore and then sealing the wellbore below a desired depth to prevent egress of the introduced fluids while allowing removal of a portion of a work string from the wellbore.
2. Description of the Related Art
In oil and gas wells, it may be desirable to inject a fluid into the well to enhance production of hydrocarbons. For example, steam, carbon dioxide, water or other fluids may be injected into the well to maintain reservoir pressure or heat the oil to lower its viscosity.
Gas injection is one common approach in enhanced oil recovery, and may use carbon dioxide, natural gas, or nitrogen. When the subject gas is injected, the phase behavior of the mixture of gas and crude causes the desired oil displacement, swelling, or a reduction in the surface tension of the oil with the surrounding formation. Each of these makes the oil easier to produce for the formation.
Enhanced oil recovery using gas injection can present some additional problems. For example, in the event of mechanical problems with equipment already in use with the well (e.g., the pump above the system fails, a tubing leak develops, etc.), the entire tubing string may have to be removed and the operator may have to flow down the well, resulting in significant delay and expense from the well flow down. Moreover, removal of the entire tubing string potentially negates any benefits from the prior fluid introduction, because such introduced fluids would be allowed to egress through the wellbore to the surface when the tubing string is removed.